Effect of hydrogenation on microstructure of TC21 alloy

Microstructure evolution of biphase TC21 alloy before and after hydrogenation as well as dehydrogenation was investigated by XRD, OM and TEM. The results show that the amount of β phase increases gradually as the hydrogen content increases; fcc δ hydrides appear when the hydrogen content reaches above 0.319%. Hydrides mainly precipitate by eutectoid transformation through diffusion during the cooling process after high-temperature hydrogenation. Because of the lattice distortion caused by eutectoid transformation, recrystallization occurs after the dehydrogenation, so the grains are refined and become much more homogenous.